PLoS One. 2019 Oct 4;14(10):e0223430. doi: 10.1371/journal.pone.0223430. eCollection 2019. Macrophage PPAR-γ suppresses long-term lung fibrotic sequelae following acute influenza infection.

Huang S1, Goplen NP1, Zhu B1, Cheon IS1, Son Y1, Wang Z1, Li C1, Dai Q1, Jiang L1, Xiang M1, Carmona EM1,2, Vassallo R1,2, Limper AH1, Sun J1,2.
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1 Thoracic Diseases Research Unit, Division of Pulmonary and Critical Care Medicine, Department of Medicine, Mayo Clinic College of Medicine and Science, Rochester, Rochester, Minnesota, United States of America. 2 Department of Immunology, Mayo Clinic College of Medicine and Science, Rochester, Rochester, Minnesota, United States of America.


Influenza virus causes a heterogeneous respiratory infectious disease ranging from self-limiting symptoms to non-resolving pathology in the lungs. Worldwide, seasonal influenza infections claim ~500,000 lives annually. Recent reports describe pathologic pulmonary sequelae that result in remodeling the architecture of lung parenchyma following respiratory infections. These dysfunctional recovery processes that disproportionately impact the elderly have been understudied. Macrophages are involved in tissue remodeling and are critical for survival of severe influenza infection. Here, we found intrinsic deficiency of the nuclear receptor PPAR-γ in myeloid cells delayed the resolution of pulmonary inflammation following influenza infection. Mice with myeloid cell-specific PPAR-γ deficiency subsequently presented with increased influenza-induced deposition of pulmonary collagen compared to control mice. This dysfunctional lung remodeling was progressive and sustained for at least 3 months following infection of mice with myeloid PPAR-γ deficiency. These progressive changes were accompanied by a pro-fibrotic gene signature from lung macrophages and preceded by deficiencies in activation of genes involved with damage repair. Importantly similar aberrant gene expression patterns were also found in a secondary analysis of a study where macrophages were isolated from patients with fibrotic interstitial lung disease. Quite unexpectedly, mice with PPAR-γ deficient macrophages were more resistant to bleomycin-induced weight loss whereas extracellular matrix deposition was unaffected compared to controls. Therefore PPAR-γ expression in macrophages may be a pathogen-specific limiter of organ recovery rather than a ubiquitous effector pathway in response to generic damage.

PMID: 31584978 DOI: 10.1371/journal.pone.0223430
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